Functional thin film with a mixed layer, piezoelectric device, ink jet recording head using said piezoelectric device, and ink jet printer using said recording head

ABSTRACT

The present invention is to produce a piezoelectric device with which the number of production processes can be reduced and reliability can be improved. A piezoelectric device ( 40 ) comprises one or more piezoelectric thin film layers ( 43 ) and 2 or more electrode layers ( 42  and  44 ). Mixed layers ( 512, 523,  and  534 ) where the components of adjacent layers are mixed are formed between the respective layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a method of producing a piezoelectricdevice used in ink jet recording heads, etc., and in particular, to amethod of producing a piezoelectric device, etc., by means of whichcrystallization of the entire layer-built structure can be performed allat once and productivity thereby raised, and its products.

2. Description of the Related Art

Piezoelectric devices are elements with electric equipment conversioncapability and are made by sandwiching a piezoelectric ceramic such ascrystalline lead zirconate titanate (PZT), etc., between electrodes. Inorder to produce this piezoelectric device, a diaphragm layer, bottomelectrode layer, piezoelectric thin film layer, and a top electrodelayer are formed in succession on a substrate. In conventional methodsof producing piezoelectric devices, a different method is used toproduce each layer because the composition of each layer is different.For instance, the diaphragm if formed by the thermal oxidation method,while the electrode layers are formed by sputtering, etc. Moreover, theso-called sol-gel method is used to produce the piezoelectric thin filmlayer. By means of the sol-gel method, a sol, or the organic metalprecursor, is applied, the sol is dried and pyrolyzed, and finally, theproduct is heat treated at a high speed and thereby crystallized.

Methods of producing thin films in general are further discussed in, forinstance, Phillips J. Res. 47('93), pp. 263-285, etc.

Nevertheless, by means of conventional methods of producingpiezoelectric devices, the thin film of one layer is completed and thenthe film of the next layer is formed and therefore, there is a problemin that the structure of each layer is completely crystallized andadhesion between the layers is weak. When adhesion between the layers ispoor, peeling occurs during the production process, leading to pooryield, and peeling occurs during use, resulting in poor reliability.Therefore, there is a demand for a method of production that results instrong adhesion.

Moreover, since each layer is as it is being crystallized, there areinevitably many processes needed to complete the piezoelectricstructure. Because there are many processes, there is naturally anincrease in the production cost. Therefore, there is a demand for aproduction method with few processes.

SUMMARY OF THE INVENTION

Thereupon, a method whereby a piezoelectric device of a piezoelectricceramic that has been applied to a substrate and pyrolyzed is placed ina specific alkali solution and crystallized is recorded in “Applicationof Hydrothermal Mechanism for Tailor-Making Perovskite Titanate Films,”IEEE Proc. of the 9th Int'l Symp. on Electrets, Shanghai, China,September 25-30, pp. 617-622 (1996), W-ping Xu, Masanori Okuyama, et al.This method of crystallization in an alkali solution is called thehydrothermal method. When compared to the sol-gel method crystallizationat a relatively low temperature is possible by means of thishydrothermal method and therefore, there are a number of advantages tothis method. The inventors of the present invention hit upon the ideathat a piezoelectric device with a multi-layered structure could becrystallized all at once by using this hydrothermal method andsuccessfully completed experiments with this production methodconfirming this point.

In light of the aforementioned facts, a first objective of the presentinvention is to present a functional thin film with high adhesionbetween layers and high reliability, a piezoelectric device, an ink jetrecording head and a printer.

A second objective problem of the present invention is to present amethod of producing a piezoelectric device and a method of producing anink jet recording head, both of which have fewer production processesthan conventional production methods and therefore have a lowerproduction cost.

The invention that solves the aforementioned first objective is afunctional thin film, characterized in that a mixed layer where thecomponents of thin film layers made of different components are mixedtogether is formed between the respective thin film layers. This film isnot only “functional thin film,” but also film that is used for anypurpose for which many thin films are used. There is a region of aspecific thickness where the components of two layers are mixed at theinterface between the respective layers of the thin film structure.

Another invention that solves the aforementioned first objective is apiezoelectric device, characterized in that it comprises at least one(1) piezoelectric thin film layer and two (2) electrode layers, and amixed layer that is a mixture of the components of adjacent layers isformed between the respective layers. The crystals of the two layers areintricately intertwined in the mixed layer and therefore, adhesionbetween the layers is high.

Still another invention that solves the aforementioned first objectiveis a piezoelectric device that further comprises at least one (1)diaphragm layer, with a mixed layer that is a mixture of the componentsof the aforementioned diaphragm layer and the adjacent electrode layerformed in between the respective layers.

Thickness of the aforementioned mixed layers is, for instance, 5 nm orthicker. By means of conventional production methods, thickness of thepart where the compositions are mixed was less than 3 nm and therefore,adhesion between layers is improved by the presence of this thick mixedlayer.

For instance, the metal alkoxide that comprises the piezoelectric thinfilm layers is any piezoelectric ceramic selected from lead zirconatetitanate (Pb(Zr, Ti)O₃: PZT), lead lanthanum titanate ((Pb, La)TiO₃),lead lanthanum zirconate ((Pb, La)ZrO₃), lead lanthanum zirconatetitanate ((Pb, La)(Zr, Ti)O₃: PLZT), or lead magnesium niobate zirconatetitanate (Pb(Mg, Nb)(Zr, Ti)O₃: PMN-PZT).

For instance, the piezoelectric device of the present invention has two(2) or more piezoelectric thin film layers and three (3) or moreelectrode layers and is made by sandwiching at least one of thepiezoelectric thin films between electrode layers. This type ofstructure is generally called a bimorph.

Still another invention that solves the aforementioned first objectiveis an ink jet recording head with the piezoelectric device of thepresent invention as the piezoelectric actuator. For instance, it has

a) a pressure chamber structure that forms the pressure chamber,

b) a diaphragm on one side of the pressure chamber, and

c) a piezoelectric device that is placed facing the diaphragm in thepressure chamber and is made so that it deforms the aforementioneddiaphragm.

Another invention of the present application that solves theaforementioned first objective is a printer that has the ink jetrecording head of the present invention as a printing means. Forinstance, it has

a) a recording medium conveyor that is made so that it is possible tofeed in and carry out the recording medium and

b) a head control circuit by means of which the ink jet recording headprints at any desired position of the recording medium that has been fedby the recording medium conveyor.

Still another invention that solves the aforementioned second objectiveis a method of producing a piezoelectric device with at least one (1)piezoelectric thin film layer and at least two (2) electrode layers,characterized in that it comprises

a) the process whereby amorphous piezoelectric thin film layers, whichare the amorphous state of each of the piezoelectric thin film layers,are formed,

b) the process whereby amorphous electrode layers, which are theamorphous state of each of the electrode layers, are formed, and

c) the process whereby after each amorphous piezoelectric thin filmlayer and each amorphous electrode layer have been laminated,hydrothermal synthesis is performed to crystallize the amorphouspiezoelectric thin film layers and the amorphous electrode layers.

Moreover, another invention that solves the abovementoned secondobjective is a method of producing a piezoelectric device that furthercomprises at least one diaphragm. This method further comprises theprocess whereby an amorphous diaphragm, which is the amorphous state ofthe diaphragm layer, is formed and whereby once the amorphous diaphragmlayer, as well as each of the amorphous piezoelectric thin film layersand each of the amorphous electrode layers, have been laminated, theaforementioned amorphous diaphragm, amorphous piezoelectric thin filmlayers, and amorphous electrode layers are crystallized by hydrothermalsynthesis in the process of hydrothermal synthesis.

For instance, the aforementioned process of forming the amorphouspiezoelectric thin film layer comprises the process whereby precursormade from an organic metal solution is applied by the sol-gel method,the MOD (metal-organic deposition) method, or the coprecipitation methodand the process whereby said precursor is dried and pyrolyzed.

For example, by means of the process whereby the aforementionedprecursor is dried and pyrolyzed, the precursor is dried at 150° C. to200° C. and the dried precursor is pyrolyzed at 300° C. to 500° C.

By means of the aforementioned hydrothermal synthesis process, forinstance, the pyrolyzed precursor is immersed in a specific alkalinesolution and crystallization is promoted under specific conditions.

The aforementioned alkaline solution here comprises any of KOH, Ba(OH)₂,Ba(OH)₂+Pb(OH)₂ or KOH+Pb(OH)₂.

The aforementioned specific conditions of the hydrothermal process arefor instance, a temperature of 100° C. to 200° C. and pressure of 10atmospheres or less.

By means of the present invention, a structure is made whereby amorphouspiezoelectric thin film layers are sandwiched by amorphous electrodelayers by repeating the process whereby the aforementioned piezoelectricthin film layers are formed at least two (2) times or more and repeatingthe process whereby the aforementioned amorphous electrode layers areformed at least three (3) times or more.

Moreover, yet another invention that solves the aforementioned secondproblem is a method of producing an ink jet recording head comprisingthe piezoelectric device made by the production method of the presentinvention, and is a method of producing an ink jet recording headcomprising

a) the process whereby a diaphragm is formed on one surface of asubstrate,

b) the process whereby a piezoelectric device is made on the diaphragm,and

c) the process whereby the substrate is etched and a pressure chamber isformed so that the diaphragm with the piezoelectric device will form oneside of the pressure chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section that describes the layer structure of thepiezoelectric device of a first embodiment of the present invention.

FIGS. 2A-2E are cross sections of the production process that describesthe method of producing a piezoelectric device of the present invention.

FIGS. 3A-3C are cross sections of the production process that describesthe method of producing an ink jet recording head of the presentinvention.

FIG. 4 is a cross section that describes the layer structure of thepiezoelectric device of a second embodiment of the present invention.

FIG. 5 is an oblique view describing the structure of the printer of thepresent invention.

FIG. 6 is a partial oblique cross section of the ink jet recording headof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiments of the present invention will be described whilereferring to figures. The present embodiment describes the layerstructure of a piezoelectric device as a functional thin film. Itpertains to a piezoelectric device that was produced by the hydrothermalmethod, and an ink jet recording head and printer that use this element.

(First embodiment)

First, the structure of a printer that uses an ink jet recording headwith the piezoelectric device of the present invention will bedescribed. As shown in FIG. 5, the printer 100 of this embodiment hastray 3, paper outlet 4, and operating button 9 in body 2 so that it canfunction as a line printer. Ink jet recording head 1, feed mechanism 6,and control circuit 8 further comprise the inside of body 2.

Ink jet recording head 1 comprises the piezoelectric device made by themethod of the present invention. This head 1 is a head for line printersin particular and is formed at a length that will cover the width of thepaper that can be fed. That is, this head is formed to size (length) notpossible with conventional printers by using the production method ofthe present invention. Ink jet recording head 1 is made so that ink issprayed from a nozzle that is set at a width of the paper that will beused in accordance with spray signals Sh that are fed from controlcircuit 8.

Body 2 is the receptacle for head 1. Feed mechanism 6 is placed so thatit can feed paper 5 from tray 3 and ink jet recording head 1 for lineprinters is placed so that it can print over the entire width of paper5. Tray 3 is made so that paper 5 can be fed to feed mechanism 6 beforeprinting and paper outlet 4 is the opening from which paper 5 that hasbeen printed is retrieved.

Feed mechanism 6 comprises motor 600, rollers 601 and 602 and amechanical structure not shown. Motor 600 is made so that it can turn inresponse to the drive signals Sd fed from control circuit 8. Themechanical structure is made so that the turning force of motor 600 canbe transmitted to rollers 601 and 602. Rollers 601 and 602 turn when theturning force from motor 600 is transmitted and paper 5 mounted in tray3 is thereby pulled by this turning and fed so that it can be printedwith head 1.

Although not shown, control circuit 8 comprises a CPU, ROM, RAM,interface circuit, etc., and is such that drive signals Sd can be fed todrive mechanism 6 and spray signals Sh can be fed to ink jet recordinghead 1 in response to printing data obtained from a computer via aconnector, which is not shown. Moreover, control circuit 8 is such thatthe drive mode can be set and reset, etc., in response to the operatingsignals from operating panel 9.

Next, the structure of the ink jet recording head of the presentinvention will be described. Ink jet recording head 1 comprises nozzle11, pressure chamber substrate 20, and diaphragm 30, as shown in theoblique and partial cross section diagram of the main part in FIG. 6.This head is an on-demand piezoelectric jet head. However, the head ofthe present invention is not limited to an on-demand head and it canalso be a continuous printer head with which ink is continually sprayedand deposition of the ink is controlled by a deflecting electrode, or itcan be a bubble head with which ink is sprayed by air bubbles.

Pressure chamber substrate 20 comprises cavity (pressure chamber) 21,side (wall) 22, reservoir 23, and feed opening 24. Cavity 21 is thecavity for the ink that will be sprayed, etc., and is formed by etchinga substrate made of silicon, etc. Wall 22 is made so that it dividescavity 21 in two. Reservoir 23 is the flow path for filling ink in eachcavity 21. Feed opening 24 is formed so that it is possible to introduceink from reservoir 23 into each cavity 21.

Furthermore, the shape of cavity 21, etc., can be changed in accordancewith the ink jet system. For instance, it can be a flat Kyser shape or acylindrical Zoltan shape. Moreover, the cavities can be 1-chamber or2-chamber cavities.

Nozzle plate 10 is glued to one side of pressure chamber substrate 20 sothat its nozzle hole 11 corresponds to each cavity 21 in pressurechamber substrate 20. Pressure chamber substrate 20 to which nozzleplate 10 has been glued is further held in a receptacle that is notillustrated to complete ink jet recording head 1.

Diaphragm 30 is glued to the other side of pressure chamber substrate20. Piezoelectric device 40 is placed at this diaphragm 30. Ink tankopening 31 is placed at this diaphragm so that the ink held in the inktank, which is not illustrated, can be fed to inside pressure chambersubstrate 20.

FIG. 1 shows a cross section that further explains the actual structureof the ink jet recording head and piezoelectric device of the presentinvention. This cross section is an enlarged view of the cross sectionof one of the piezoelectric devices in the layered structure as seenfrom I—I in FIG. 6. As shown in the top of FIG. 1, diaphragm 30 is madeby building diaphragm layer 41 and bottom electrode layer 42, andpiezoelectric device 40 is made by layering piezoelectric thin filmlayer 43 and top electrode layer 44. In particular, this ink jetrecording head 1 is made with piezoelectric device 40, cavity 21 andnozzle 11 communicating at a constant pitch so that the entire width ofthe paper to be printed can be covered. This pitch to the nozzle can bechanged as needed in accordance with the desired printing precision. Forinstance, it can be set to obtain 400 dpi.

Diaphragm layer 41 is made from a material that is not conductive, suchas silicon dioxide (SiO₂) and zirconium oxide (ZrO₂), etc., and is madeso that it can deform when voltage is applied to the piezoelectric layerand thereby instantly increase the pressure inside cavity 21. It must bemade from a material that can be crystallized by hydrothermal synthesisif the diaphragm layer is to be crystallized by hydrothermal synthesis.

Bottom electrode layer 42 is one electrode for applying voltage to thepiezoelectric layer and it is made from a material that is conductive,such as tin oxide (SnO) or vanadium oxide (VO₂), etc. A material thatcan be crystallized by hydrothermal synthesis is particularly necessary.Bottom electrode layer 42 is formed in the same region as diaphragmlayer 41 so that it can serve as a common electrode to severalpiezoelectric devices 40 formed on pressure chamber substrate 20.However, it can also be formed to the same size as piezoelectric thinfilm layer 43, that is, to the same shape as top electrode 44. Topelectrode layer 44 is the other electrode for applying voltage to thepiezoelectric layers and it is made from a material that is conductive,such as tin oxide (SnO) or vanadium oxide (VO₂), etc. It must be amaterial that can be crystallized by hydrothermal synthesis.

Piezoelectric device 40 is made from crystals of a piezoelectric ceramicwith, for instance, a perovskite structure, and is formed to a specificshape on diaphragm 30. In particular, piezoelectric thin film 43 of thepresent invention is crystallized by the hydrothermal method andtherefore, crystal grains with a columnar shape (columnar crystalgrains) either display [110] orientation in the direction of filmthickness, or they take on inconsistent random orientation in thedirection of the crystals. For instance, these columnar crystal grainshave a width parallel to the electrode film, that is, an average graindiameter, within a range of 100 nm to 15,000 nm. The face ofpiezoelectric thin film 43 that will connect with top electrode layer 44is smooth in comparison to conventional hydrothermal treatment. Forinstance, maximum height of surface roughness is 20 nm or less. It ischaracterized in that there is little surface roughness due to the factthat this hydrothermal method is used to concomitantly with the sol-gelmethod.

The composition of the piezoelectric thin film layers is, for instance,any piezoelectric ceramic selected from lead zirconate titanate (Pb(Zr,Ti)O₃: PZT), lead lanthanum titanate ((Pb, La)TiO₃), lead lanthanumzirconate ((Pb, La)ZrO₃), lead lanthanum zirconate titanate ((Pb,La)(Zr, Ti)O₃: PLZT), or lead magnesium niobate zirconate titanate(Pb(Mg, Nb)(Zr, Ti)O₃; PMN-PZT). However, the present invention ischaracterized in its production method and the piezoelectric film layersare not limited to the aforementioned composition.

As shown in the middle of FIG. 1, a characterizing point of thestructure of the piezoelectric device of the present invention is thatit comprises mixed layers that are mixtures of the composition of twolayers between each of these layers. For example, mixed layer 512 is inbetween diaphragm layer 41 and bottom electrode layer 42 andpiezoelectric thin film layer 43, and mixed layer 534 is in betweenpiezoelectric thin film layer 43 and top electrode layer 44. These mixedlayers form interface areas where the crystal grains in the upper andlower layers are mixed together, as shown in the bottom of FIG. 1. Thismixed layer is formed by mixing the two compositions together andpromoting crystallization when the layers are laminated in an amorphousstate in accordance with the production method described below.

The printing operation will now be described using ink jet recordinghead 1 with the aforementioned piezoelectric device 40. When drivesignals Sd are output from control circuit 8, drive mechanism 6 isturned on and conveys paper 5 to where it can be printed by head 1. Ifspray signals Sh are not fed from control circuit 8, voltage will not beapplied to piezoelectric device 40 between bottom electrode layer 42 andtop electrode layer 44 and as a result, there will be no deformation ofpiezoelectric thin film layer 43. Therefore, there will be no changes inpressure in cavity 21 where piezoelectric device 40 is placed when spraysignals Sh are not fed and ink drops will not be sprayed from nozzlehole 11.

On the other hand, when spray signals Sh are fed from control circuit 8and constant voltage is applied to piezoelectric device 40 betweenbottom electrode layer 42 and top electrode layer 44, deformation ofpiezoelectric thin film layer 43 occurs. Diaphragm 30 will bendconsiderably in cavity 21 where piezoelectric device to which spraysignals have been fed is set up. Therefore, pressure inside cavity 21instantly increases and ink droplets are sprayed from nozzle hole 11.Spray signals Sh can be individually fed to piezoelectric devices whereprinting has been performed by fine heads making it possible to printany character or figure.

(Description of production methods)

Next, the method of producing the piezoelectric device will be describedtogether with the method of producing the ink jet recording head. FIG. 2is cross section diagrams showing the process of producing thispiezoelectric device.

Process of diaphragm layer formation (FIG. 2A): The diaphragm layerformation process is the process whereby diaphragm layer 41 is formed onsilicon substrate 20. A thin long silicon substrate that has been formedfor line printers is used as silicon substrate 20. Thickness is, forinstance, 200 μm so that height of the walls will not be too high.Diaphragm layer 41 is formed to a thickness of, for instance, 1 μm.Conventional thermal oxidation, etc., is used to produce the insulatinglayer. Furthermore, when zirconium oxide, etc., is used for thediaphragm, this sol can be applied to a specific thickness and thencrystallized by hydrothermal synthesis later.

Bottom electrode layer formation process (FIG. 2B): By means of theprocess of forming the bottom electrode layer, bottom electrode layer 42is formed on diaphragm layer 41. A sol for forming the bottom electrodelayer is first made. This sol is produced by dissolving tin chloride(SnCl₂·H₂O) to a specific concentration, for instance, 0.5 Mmol/l inethanol and then doping it with zirconium isopropoxide (Zr(O-i-C₃H₇)₄)at a concentration of 1 to 2 mol % in terms of the tin. The method ofproducing the sol is not limited to the aforementioned method.

Next, the aforementioned sol is applied to diaphragm layer 41 by anyapplication method, such as spin coating, die coating, spray coating,roll coating, etc. For example, after applying the sol to a thickness of2 μm by spin coating, the product is heated for a specific amount oftime (for instance, 10 minutes) at a specific temperature (for instance,180° C.) in order to evaporate the solvent. The dry sol is thenpyrolyzed for a specific amount of time (for instance, 10 minutes) at aspecific temperature (for instance, 300° C.) in order to furthereliminate organic matter that has mixed in the metal elements. The metalelement Zr in the dopant acts to improve conductivity of bottomelectrode layer 42 that has been treated and formed.

Piezoelectric thin film layer formation process (FIG. 2C): Thepiezoelectric thin film formation process is the process whereby apiezoelectric thin film layer made from several thin films is formed byrepeatedly applying sol and then drying and pyrolyzing the sol. First, asol for the piezoelectric ceramic that will be the starting material forthe piezoelectric thin film layer is made. For instance, using2-n-butoxyethanol as the main solvent, lead acetate trihydrate(Pb(CH₃COO)₂·3H₂O), titanium tetraisopropoxide (Ti(CH₃CH₂CH₂O)₄),magnesium pentaethoxyniobium (Nb(OC₂H₅)₅), tetra-n-propoxyzirconium(Zr(O-n-C₃H₇)₄) and magnesium acetate (Mg(CH₃COO)₂·5H₂O) are dissolvedin a solvent to which iminodiethanol has been added to produce thepiezoelectric sol. However, the method of producing the sol is notlimited to this production method.

Next, the sol that has been produced as previously explained is appliedto bottom electrode layer 42 to a specific thickness. Applications canbe performed by the aforementioned methods. For example, when spincoating is used, the sol is applied for 30 seconds at 500 rpm, for 30seconds at 1500 rpm and finally, for 10 seconds at 500 rpm. Each metalatom comprising the PZT will be dispersed as organic complex during theapplication stage. Once application is completed, the product is driedfor a specific time (for instance, 10 minutes) at a specific temperature(for instance, 180° C.). After drying, the product is pyrolyzed for aspecific time (for instance, 10 minutes) at a specific temperature (forinstance, 300° C.) in air. Each process of application of sol drying andpyrolyzing is repeated several times, for instance, 20 times, to buildpiezoelectric thin film layers 43 to a specific thickness (for instance,2 μm) Multi-layering is done in order to prevent cracking whileproducing a thicker film.

Top electrode layer formation process (FIG. 2D): The top electrodeformation process is a process whereby top electrode layer 44 is formedon piezoelectric thin film layer 43. Using the same sol as used to formthe aforementioned bottom electrode layer, sol is applied to a specificthickness (for instance, 0.2 μm, by the same spin coating method as usedfor the bottom electrode formation process, etc. Moreover, the productis then dried and pyrolyzed as in the aforementioned bottom electrodeformation process.

Hydrothermal synthesis process (FIG. 2E): The hydrothermal treatmentprocess is the process whereby crystallization of the aforementionedelectrode layers and piezoelectric thin film layer are performed at thesame time by heat treatment in a specific alkali solution. First,alkaline solution 101 is filled into tank 100 that is made so thatpressure can be increased. The layer structure of the piezoelectricdevice that has been laminated by the aforementioned process is immersedin tank 100 and crystallization is promoted under specific conditions inan autoclave. The treatment solution can be any of KOH, Ba(OH)₂, a mixedsolution of Ba(OH)₂ and Pb(OH)₂, or a mixed solution of KOH and Pb(OH)₂as the solute when an alkaline solution is used. This is because it hasbeen confirmed that piezoelectric ceramics crystallize in these alkalinesolutions. The concentration of the alkali solution is adjusted to aconcentration less than 2 Mmol/liter. If the concentration exceeds thisconcentration, the alkali will be strong and may corrode thepiezoelectric thin film layer and substrate, etc. For instance, theconcentration is adjusted to 0.5 Mmol/liter. The hydrothermal treatmenttemperature is set at 100 to 200° C. If temperature is lower than thisrange, crystallization will not be promoted and if temperature is higherthan this range, etching of the piezoelectric thin film layer andsilicon substrate will occur. For instance, treatment temperature is setat 140° C. The pressure of hydrothermal treatment is set between 2kg/cm² to 10 kg/cm². If pressure is outside this range, good crystalswill not be obtained. Pressure is set at, for instance, 4 kg/cm². Thehydrothermal treatment time is between 10 minutes and 60 minutes. Iftreatment time is shorter, crystallization will not be complete and ifthe crystallization time is longer, there is a chance that thepiezoelectric thin film layer and substrate will be eroded. Forinstance, treatment time is set at 30 minutes.

Crystallization of each layer is promoted by the aforementionedhydrothermal synthesis treatment. Each layer was laminated as is withoutbeing crystallized and therefore, there is a part at the interfacebetween adjacent layers where the compositions of the two layers aremixed before this hydrothermal treatment. By submitting this mixed partto hydrothermal synthesis, crystal grains of each composition are formedand, as shown in FIG. 1, mixed layers 523 and 534 where the crystalgrains of both layers are finely distributed are formed. Mixed layer 512is also formed when the diaphragm layer is formed by sol application.

By means of the aforementioned process, the layer structure of thepiezoelectric clement is completed. Since heat treatment to promotecrystallization is not necessary in any of the aforementioned productionprocesses, the number of processes as a whole is reduced. Therefore,cost is reduced. Moreover, piezoelectric device 40 that was produced bythe aforementioned production method has mixed layers between the layersand therefore, adhesion between layers is extremely high. Consequently,there is no peeling of the layers and the yield of the productionprocesses is improved. Moreover, there is no peeling between layers ofthe piezoelectric device that is the product and therefore reliabilityis improved and life can be prolonged.

In addition, in order to give the piezoelectric device the desiredshape, the layer structure made as described above is formed into thedesired shape by etching, etc., in accordance with the device in whichthe piezoelectric device will be used. By means of the presentembodiment, the piezoelectric device is used as the actuator of an inkjet recording head and therefore, it will be further treated by theprocess shown in the cross section in FIG. 3.

Etching process (FIG. 3A): The etching process is the process wherebypiezoelectric device 40 is formed. First, aforementioned thepiezoelectric thin film layer 43 of the aforementioned piezoelectricdevice and top electrode layer 44 are masked so that they are the sameshape as the cavity formed in pressure chamber substrate 20. Thenetching is performed around this mask to obtain piezoelectric device 40.For more detail, resist material of a uniform thickness is applied bythe spinner method, spraying, etc. Then a mask is formed to the shape ofthe piezoelectric device and exposure and development are performed toform a resist pattern on the top electrode layer 44. The mask is formedas needed, depending on whether the resist material is a positive resistor a negative resist. Moreover, top electrode layer 44 and piezoelectricthin film layer 43 is etched and removed by ion milling or dry etching,etc., which are normally used. Piezoelectric device 40 suitable for anink jet recording head can be made as described above.

Pressure chamber formation process (FIG. 3B): The pressure chamberformation process is the process whereby cavity 21 is formed by etchingon the other side of chamber pressure substrate 20 in whichpiezoelectric device 40 has been formed. For instance, anisotropicetching, anisotropic etching using an active gas, such as parallelplate-type reactive ion etching, etc., is used and etching of the spacecavity 21 is performed from the opposite side of the surface wherepiezoelectric device 40 has been formed. The part that remains unetchedbecomes wall 22.

Nozzle plate gluing process (FIG. 3C): The nozzle gluing process is theprocess whereby nozzle plate 10 is glued with adhesive to siliconsubstrate 20 after etching. When glued together, each nozzle hole 11 isaligned so that it matches the empty space of each cavity 21. Finally,pressure chamber substrate 20 to which nozzle plate 10 is glued isattached to the receptacle and ink jet recording head 1 is completed.

Furthermore, when etching is performed on the nozzle plate and pressurechamber substrate as one unit, the process of gluing the nozzle plate isunnecessary. This is because the pressure chamber substrate is etched toa shape so that it will serve as both the nozzle plate and the pressurechamber plate and the nozzle holes will in the end match the cavities.

EXAMPLES

A piezoelectric device with lead zirconate titanate(Pb(Zr_(0.56)Ti_(0.44))O₃: PZT) as the piezoelectric thin film layerswas made as Example 1 of the aforementioned production method. Startingat the top, the layer-built structure was top electrode layerSnO/piezoelectric thin film layer PZT/bottom electrode layerSnO/diaphragm layer SiO₂/pressure chamber substrate Si. Only thediaphragm layer was made by thermal oxidation. The rest of the layerswere applied by spin coating. Crystallization of the electrode layer andthe piezoelectric thin film layers was eventually performed byhydrothermal synthesis.

Moreover, a piezoelectric device wherein, starting from the top, thelayer-built structure was top electrode film VO₂/piezoelectric thin filmlayer PZT/bottom electrode layer VO₂/diaphragm layer SiO₂/pressurechamber substrate Si was made as Example 2. By means of this example,the composition of the top electrode layer and the bottom electrodelayer are different than the aforementioned SnO. Therefore, a sol wasformed by dissolving triethoxyvanadyl (VO(OC₂H₅)₃) and titaniumtetraisopropoxide (Ti(CH₃CH₂CH₂O)₄) as dopant in ethanol in place of theaforementioned SnO sol. The sol application method, etc., was the sameas for the SnO electrode layer formation method.

Moreover, a piezoelectric device wherein, starting from the top, thelayer-built structure was top electrode layer SnO/piezoelectric thinfilm layer PZT/bottom electrode layer SnO/diaphragm layer ZrO/pressurechamber substrate Si, was made as Example 1. By means of this example,the diaphragm layer was made by sol application instead of thermaloxidation. The sol used to form the diaphragm layer was made bydissolving tetra-n-propoxyzirconium (Ti(CH₃CH₂CH₂O)₄) in2-n-butoxyethanol. The sol was repeatedly applied 10 times by spincoating to a diaphragm layer thickness of 1 μm. By means of the presentexample, the diaphragm layer was also formed from a sol and therefore, amixed layer was also formed between the diaphragm layer and the bottomelectrode layer.

By means of the aforementioned example, application was mainly by spincoating during the production processes and therefore, the methodrequired less production equipment than conventional methods. Moreover,the only heat treatment was one hydrothermal treatment and therefore,the number of processes was reduced. Moreover, none of the filmdegradation due to repeated heat treatment that is seen withconventional methods was observed, proving that the production method ofthe present invention efficiently improves reliability.

(Advantages)

a) By means of the present embodiment, almost all of the layerscomprising the piezoelectric device are formed by application andtherefore, there is no need to use many pieces of production equipmentand a reduction in cost can be expected.

b) By means of the present embodiment, heat treatment is not appliedevery time a layer is formed. Hydrothermal synthesis treatment isperformed once layering is completed and therefore, there is a reductionin the number of production processes and a reduction in cost can beexpected.

c) By means of the present embodiment, the entire unit is crystallizedall at once after each layer has been laminated before crystallizationand therefore, there is a mixed layer where the compositions of twolayers are mixed together between each layer. The crystals contained inthe two layers are intricately intertwined in this mixed layer and as aresult, adhesion between the layers is good and there is no peeling,etc. Consequently, yield is good during production and a reduction incost can be expected. Moreover, as a product, reliability is good andlife is long.

d) By means of the present embodiment, high-temperature heat treatmentis not performed for the hydrothermal synthesis treatment and therefore,elements of the bottom electrode will not diffuse into the piezoelectricthin film and degradation of piezoelectric device properties can beprevented.

e) By means of the present embodiment, high-temperature heat treatmentis not performed and therefore, there are no changes in properties andthermal stress is not applied to any of the films and reliability of thepiezoelectric device and ink jet recording head can be improved.

f) By means of the present embodiment, high-temperature heat treatmentis not necessary and therefore, the incidence of defects is low.Therefore, cost can be reduced.

g) By means of the present embodiment, little internal stress (includingthermal stress) is produced because high-temperature heat treatment isnot performed and therefore, even when a piezoelectric device with alarge surface is produced, cracking will not occur. That is, an ink jetrecording head that is suitable for large surface area printingequipment such as line printers, etc., can be presented.

(Embodiment 2)

The present embodiment of the present invention pertains to apiezoelectric device with a layer-built structure as a so-calledbimorph. FIG. 4 shows a cross section that describes the layer-builtstructure of the piezoelectric device of the present embodiment. Thecross section is an enlarged view of the cross section of onepiezoelectric device from the layer structure as seen from A—A in FIG.6. The parts of the layer structure that are the same as inaforementioned Embodiment 1 are represented by the same symbol and theirdescription here is omitted.

However, piezoelectric device 40 b of the present embodiment furthercomprises middle layer 45 and piezoelectric thin film layer 46 betweenpiezoelectric thin film layer 43 and top electrode layer 44, as shown inFIG. 4. This type of layer-built structure is generally called a bimorphand has the effect of diffusing strain.

Middle layer 45 is made by the same composition and production method asused for bottom electrode layer 42 and top electrode layer 44. Forinstance, it can be made from SnO or VO₂. Piezoelectric thin film layer46 can be the same as piezoelectric thin film layer 43, or it can have adifferent composition and a different film thickness.

Mixed layer 535 is made between piezoelectric thin film layer 43 andmiddle layer 45, mixed layer 556 is made between middle layer 45 andpiezoelectric thin film layer 46, and mixed layer 564 is made betweenpiezoelectric thin film layer 46 and top electrode layer 44. These mixedlayers are layers where crystals from the two layers sandwiching thismixed layer are mixed together, as explained in aforementionedEmbodiment 1. Thickness of the mixed layer can be the same as explainedin aforementioned Embodiment 1.

The process used to produce piezoelectric device 40 with theaforementioned layer-built structure can also be in accordance withaforementioned Embodiment 1. However, once the sol for piezoelectricthin film layer 43 has been applied and dried and pyrolyzed, middlelayer 45 is formed by the same method as used for the top electrode inplace of the top electrode layer. After middle layer 45 is formed,electrode thin film 46 is further formed by the same method as used toform piezoelectric thin film layer 43. The hydrothermal synthesisprocess can be the same as used in aforementioned Embodiment 1. By meansof this production process, each layer is laminated beforecrystallization and the materials in the two layers are mixed, afterwhich crystallization is promoted by hydrothermal synthesis andtherefore, production processes can be omitted and cost can be reduced.Adhesion between the layers is high because a mixed layer is present inbetween each layer and as a result, there is little peeling of layers.Consequently, yield can be improved during the production processes andreliability of the product can be improved and its life can beprolonged.

Furthermore, the present invention is not limited to the aforementionedlayer structure, and it can have more layers. That is, by means of theaforementioned embodiment, there are 2 piezoelectric thin film layers,but there can be 3 or more layers. The electrode layers, including themiddle layer, are increased by 1 layer every time the piezoelectric thinfilm layer is increased by one layer. In the end, there are n+1electrode layers when there are n number (n is a natural number) ofpiezoelectric thin film layers. The method of aforementioned Embodiment1 can be repeatedly used as the production method

Other Modified Examples

The present invention can be altered from the aforementioned embodimentsand used. For instance, the aforementioned embodiments have dealt withpiezoelectric devices as functional thin film, but they are not limitedto these functional thin film and the present invention can be used witha general thin film structure with a specific function that is severalthin films. Since there is a mixed layer between layers of differentcomponents, adhesion between two layers is extremely high and there isno peeling at the interface. Therefore, even if stress is applied to athin film that is curved, the layer structure will remain intact and afunctional thin film with high reliability that can resist changes overthe years can be presented.

Moreover, the method of producing the functional thin film uses themethod whereby the components of two layers are diffused by heattreatment to make a mixed layer wherein the components of the two layersare formed, etc.

The piezoelectric device used PZT, but it is also possible tocrystallize other ferroelectric piezoelectric ceramics by hydrothermalmethods.

The piezoelectric device made by the present invention can be used isnot only a piezoelectric device for the aforementioned ink jet recordingheads, but can also be used in the production of ferroelectricequipment, dielectric equipment, pyroelectric equipment, piezoelectricequipment, and photoelectric equipment, including nonvolatilesemiconductor memory devices, thin film capacitors, pyroelectricdetectors, sensors, surface acoustic wave optical guides tubes, opticalmemory devices, space optical modulators, diode laser frequencymultipliers, etc. That is, the piezoelectric device of the presentinvention can have an increased surface area, making cost reductionpossible. Moreover, it can be used for purposes not seen withconventional products and conventional functions can be presented lessexpensively.

By means of the present invention, there is a mixed layer that is amixture of crystal structures between each of the layers and therefore,adhesion between layers is improved. Consequently, A very reliablelong-life functional thin film, piezoelectric device, and ink jetrecording head and printer can be presented.

Moreover, by means of the present invention, the only process necessaryfor crystallization is hydrothermal synthesis, which is performed aftermany layers have been laminated and therefore, there are fewer totalproduction process than with conventional methods. Consequently, it ispossible to resent a method of producing piezoelectric devices and inkjet recording heads of reduced production cost.

The entire disclosure of Japanese Patent Applications No. 10-186679filed on Jul. 1, 1998 and No. 11-163867 filed on Jun. 10, 1999 includingspecification, claims, drawings and summary are incorporated herein byreference in its entirety.

What is claimed is:
 1. A functional thin film element comprising: afirst thin film layer formed of a first component; a second thin filmlayer formed of a second component different than said first component;and a mixed layer formed between said first and said second thin filmlayers, wherein said first and second components of said first andsecond thin film layers are mixed to form said mixed layer.
 2. Afunctional thin film according to claim 1, wherein said mixed layer hasa thickness of at least 3 nm.
 3. A functional thin film elementaccording to claim 1 comprising: two or more of said first thin filmlayers and three or more of said second thin film layers layers; whereinat least one of said first thin film layers is sandwiched between atleast two of said second thin film layers.
 4. A piezoelectric deviceformed on a bottom electrode comprising: at least one piezoelectric thinfilm layer formed on a first component; an electrode layer formed of asecond component, wherein the bottom electrode is also formed of saidsecond component, and wherein said at least one piezoelectric thin filmlayer is adjacent to said electrode layer and said bottom electrode; anda mixed layer formed between said adjacent layers, wherein said firstand second components are mixed to form said mixed layer.
 5. Apiezoelectric device according to claim 4, further comprising: at leastone diaphragm layer formed of a third component adjacent to one of saidat least two electrode layers; and a second mixed layer formed betweensaid diaphragm layer and said one of said at least two electrode layerswherein said second and third components are mixed to form said secondmixed layer.
 6. A piezoelectric device according to claim 5, whereinsaid second mixed layer has a thickness of at least 3 nm.
 7. Apiezoelectric device according to claim 4, wherein the thickness of saidmixed layer is at least 5 nm.
 8. A piezoelectric device according toclaim 4, wherein said piezoelectric thin film layer includes a metalalkoxide that is any piezoelectric ceramic selected from lead zirconatetitanate (Pb(Zr, ti)O₃: PZT), lead lanthanum titanate ((Pb, La)TiO₃),lead lanthanum zirconate ((Pb, La)(Zr, Ti)O₃: PLZT), or lead magnesiumniobate zirconate titanate (Pb(Mg, Nb)(Zr, Ti)O₃; PMN-PZT).
 9. Apiezoelectric device according to claim 4, comprising: two or more ofsaid piezoelectric thin film layers and three or more of said electrodelayers; wherein at least one of said piezoelectric thin film layers issandwiched between at least two of said electrode layers.
 10. Apiezoelectric device according to claim 4, wherein said mixed layer hasa thickness of at least 3 nm.
 11. An ink jet recording head comprising:a nozzle; a pressure chamber; a bottom electrode formed of a secondcomponent; and a piezoelectric device acting as a piezoelectric actuatorfor spraying ink from said pressure chamber through said nozzle, whereinsaid piezoelectric device includes: at least one piezoelectric thin filmlayer formed of a first component; an electrode layer formed of saidsecond component, wherein said at least one piezoelectric thin filmlayer is adjacent to said electrode layer and said bottom electrode; anda mixed layer formed between said adjacent layers, wherein said firstand second components are mixed to form said mixed layer.
 12. An ink jetrecording head according to claim 11, wherein said mixed layer of saidpiezoelectric device has a thickness of at least 3 nm.
 13. A printercomprising: an ink jet recording head including: a nozzle; a pressurechamber; a bottom electrode formed of a second component; and apiezoelectric device acting as a piezoelectric actuator for spraying inkfrom said pressure chamber through said nozzle wherein saidpiezoelectric device includes at least one piezoelectric thin film layerformed of a first component, and electrode layer formed of said secondcomponent, wherein said at least one piezoelectric thin film layer isadjacent to said electrode layer and said bottom electrode, and a mixedlayer formed between said adjacent layers, wherein said first and secondcomponents are mixed to form said mixed layer; and a control circuit forgiving signals to said ink jet recording head to spray ink.
 14. Aprinter head according to claim 13, wherein said mixed layer of saidpiezoelectric device has a thickness of at least 3 nm.